Golf balls containing interpenetrating polymer networks

ABSTRACT

The present invention is directed to a golf ball that contains an interpenetrating polymer network, or IPN, including at least two polymeric components. These IPNs may be present in any golf ball layer, although in an intermediate or cover layer in one preferred embodiment. The present invention is also directed to methods of forming a golf ball containing an IPN in one or more of the layers.

This application is a continuation of U.S. patent application Ser. No.09/833,667, filed Apr. 13, 2001, now U.S. Pat. No. 7,429,220, the entiredisclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention is directed to a golf ball that contains aninterpenetrating polymer network, or IPN, including at least twopolymeric components. The method of forming a golf ball containing anIPN in one or more of the layers is also an aspect of the presentinvention.

BACKGROUND OF THE INVENTION

Various golf balls, golf ball layers, and methods of making golf ballsare generally known in the art. The centers may be fluid-filled orsolid. Such golf balls may have a multilayer construction. Golf ballsmay have a wound layer or may be solid.

Regardless of the form of the ball, players generally seek a golf ballthat embodies a beneficial combination of properties, for example, suchas maximum distance, which requires a high initial velocity upon impact.Therefore, golf ball manufacturers are continually searching for newways in which to provide golf balls that deliver the maximum performancefor golfers of varying skill levels.

Polyurethane materials are sometimes used in golf ball layers to providea beneficial mix of properties. For example, U.S. Pat. Nos. 3,147,324;5,816,937; and 5,885,172 are directed to golf balls, or methods formaking such, having a polyurethane outer cover.

U.S. Pat. No. 4,123,061 teaches a golf ball made from a polyurethaneprepolymer of polyether, and a curing agent, such as a trifunctionalpolyol, a tetrafunctional polyol, or a diamine.

U.S. Pat. No. 5,334,673 discloses the use of two categories ofpolyurethane available on the market, i.e., thermoset and thermoplasticpolyurethanes, for forming golf ball covers and, in particular,thermoset polyurethane covered golf balls made from a composition ofpolyurethane prepolymer and a slow-reacting amine curing agent and/or adifunctional glycol.

U.S. Pat. No. 3,989,568 discloses a three-component system employingeither one or two polyurethane prepolymers and one or two polyol orfast-reacting diamine curing agents. The reactants chosen for the systemmust have different rates of reactions within two or more competingreactions.

U.S. Pat. No. 4,123,061 discloses a golf ball made from a polyurethaneprepolymer of polyether and a curing agent, such as a trifunctionalpolyol, a tetrafunctional polyol, or a fast-reacting diamine curingagent.

U.S. Pat. No. 5,334,673 discloses a golf ball cover made from acomposition of a thermosetting polyurethane prepolymer and aslow-reacting polyamine curing agent and/or a difunctional glycol.Resultant golf balls are found to have improved shear resistance and cutresistance compared to covers made from balata or SURLYN®.

U.S. Pat. No. 5,692,974 discloses methods of using cationic ionomers ingolf ball cover compositions. Additionally, the patent relates to golfballs having covers and cores incorporating urethane ionomers. Improvedresiliency and initial velocity are achieved by the addition of analkylating agent, such as t-butyl-chloride, which induces ionicinteractions in the polyurethane to produce cationic type ionomers.

PCT Publication WO 98/37929 discloses a composition for golf ball coversthat includes a blend of a diisocyanate/polyol prepolymer and a curingagent comprising a blend of a slow-reacting diamine and a fast-reactingdiamine. Improved “feel,” playability, and durability characteristicsare exhibited.

U.S. Pat. No. 5,908,358 discloses a urethane golf ball cover cured witha polyamine or glycol and an epoxy-containing curing agent. The urethanematerial in the golf ball cover also exhibits a tensile modulus of about5 ksi to 100 ksi. Improved shear resistance characteristics are seenwith these golf ball covers.

Interpenetrating polymer networks, or IPNs, are occasionally used toimprove key physical properties or to aid in the compatibilization ofthe components of a polymer mixture or blend. Different kinds of IPNsand the ways in which they may be made are available from a number ofsources in the literature, such as, for example, in Advances inInterpenetrating Polymer Networks, Volume 4, by Frisch & Klempner, andin Interpenetrating Polymer Networks by Klempner, Sperling, & Utracki.In addition, many patents describe compositions and methods forsynthesizing various types of IPNs containing various components.

U.S. Pat. No. 5,786,426 discloses an IPN based on polyisoprene andpolyurethane used for medical devices, the formation of which wasaccomplished by swelling a thermoplastic polyurethane with THF at anincreased temperature into which cis-polyisoprene was blended andperoxide initiators were dispersed for crosslinking.

U.S. Pat. No. 5,709,948 discloses a semi-IPN prepared by reactingolefinic homopolymers with epoxy resin in the presence of an epoxycurative agent, such as a triarylsulfonium hexafluorophosphate.

U.S. Pat. No. 5,674,942 discloses a homogeneous IPN having a singleglass transition temperature made by reacting a mixture of di- orpoly-amines with a di- or poly-isocyanate to form a polyurea in thepresence of acrylic ester monomers, to be polymerized with free radicalinitiators, also in the presence of tertiary amines.

U.S. Pat. No. 5,648,432 discloses a method for improving the fracturetoughness, microcracking resistance, thermal and mechanical performanceof high-temperature resistant polymers, such as polymers made frombismaleimides or imide-sulfones or polysulfones, polyamides, orpolyimides, by dispersing them in monomers or prepolymers oflow-temperature durable polymers, such as urethane-ethers,urethane-esters, ester-esters, ether-esters, ether-amides, ester-amides,silanes, siloxanes, or diene homopolymers or copolymers.

U.S. Pat. No. 5,539,053 discloses an IPN containing a glassy polymer,such as PMMA or polyacrylates, in which acrylate monomers arepolymerized with radical initiators such as azobisisobutyronitrile(AIBN) in the presence of urethane prepolymers and polyol curativeagents.

U.S. Pat. No. 5,331,062 discloses IPNs containing epoxy polymers withacrylate monomers or polyurethane precursors.

U.S. Pat. No. 5,306,784 discloses a tough, processable semi-IPN made bymixing monomer precursors of polyimides having an acetylene group withmonomer precursors of thermoplastic polyimides. Alternately, either setof the monomer precursors may be dispersed in monomer precursors of lowmodulus polymers.

U.S. Pat. No. 5,241,020 discloses the preparation of a mixture includingat least two different compounds that react with each other in theabsence of free radical initiators and at least one monomer having acarbon-carbon double bond that polymerizes in the presence of freeradical initiators. Examples of the former component includepolyurethane or poly-epoxy precursors, while examples of the lattercomponent include acrylates, methacrylates, acrylonitriles, vinylacetates, and other vinyl monomers.

U.S. Pat. No. 5,210,109 discloses rubber-modified IPNs prepared byswelling a crosslinked polymer in monomers, oligomers, or macromonomersof vinyl acrylates or other vinyl moieties, which are then polymerized.

U.S. Pat. No. 5,084,513 discloses the dissolution of a polyalkene, suchas polyethylene or polypropylene, with monomers having vinyl aromatic oracrylate-containing moieties into which a free radical initiator isadded to polymerize the monomers.

U.S. Pat. No. 4,923,934 discloses the formation of an IPN from thereaction of a blocked urethane prepolymer, a polyol, and epoxy resin,and an epoxy-catalyzing agent, such as an anhydride.

Hua et. al., in J. Polym. Sci., 1999, 37, 3568, disclose an IPN based onepoxy resin and urethane acrylate formed from an epoxy-graftedpolypropylene oxide and urethane acrylate precursors.

Japanese Patent Publication Nos. JP 62-014869 and JP 62-014870 discloseIPNs based on polybutadiene rubber crosslinked by vulcanization and anionomeric phenol-formaldehyde resin network, which IPNs are used insolid golf ball centers.

U.S. Pat. Nos. 5,542,677; 5,591,803; and 6,100,336 disclose golf ballcover compositions containing blends of neutralized carboxylicacid-containing polymers with ethylene-alkyl acrylate copolymers. Thesepatents suggest that the neutralization of the carboxylicacid-containing polymer, thus forming an ionomer, in the presence of theethylene-alkyl acrylate copolymer may result in an IPN or alternatelymay cause dynamic vulcanization.

It is desirable to improve the compatibility, as well as the thermal andmechanical properties, of polymers and/or polymer blends in the core orany layer disposed therearound in golf ball applications.

SUMMARY OF THE INVENTION

The present invention relates to an interpenetrating polymer network ina golf ball. In particular, the present invention relates to a golf ballincluding a center and a cover disposed over the center, wherein atleast one interpenetrating polymer network is present in at least aportion of the golf ball outside the center. In one embodiment, the golfball also includes at least one intermediate layer, which can optionallyinclude a tensioned elastomeric material, disposed between the cover andthe center. In another embodiment, one of the layers of the golf ballhas a foamed structure. In yet another embodiment, the golf ball centerincludes a solid sphere or a fluid-filled sphere. In still anotherembodiment, the golf ball cover includes at least an inner cover layerand an outer cover layer. Advantageously, the golf ball cover materialmay have at least one of a dimple coverage of greater than about 60percent, a hardness greater than about 15 Shore A, or a flexural modulusof greater than about 500 psi (3.4 MPa), as measured according to ASTMD6272-98, Procedure B. Where the ASTM standard calls for at least 40hours of delay before testing, the procedure is modified herein to delaytesting for about two weeks after polymer formation. Alsoadvantageously, the golf ball may have at least one of a compression nogreater than about 120 or a coefficient of restitution of greater thanabout 0.7.

In one embodiment, the golf ball includes a non-vulcanizable,non-aromatic, or non-ionomeric interpenetrating polymer network in aportion of the golf ball. For example, when the golf ball includes anon-vulcanizable IPN, a styrenic moiety can be included on a polymer ofthe IPN. In another embodiment, the IPN may contain an ionomericpolymer, provided that the ionomeric polymer does not contain acopolymer of an α-olefin and a metal-neutralized α,β-unsaturatedcarboxylic acid and is not present in a cover layer. In one preferredembodiment, the IPN may contain an ionomeric polymer, provided that theionomeric polymer does not contain a copolymer of ethylene and ametal-neutralized α,β-unsaturated carboxylic acid and is not present ina cover layer. In yet another embodiment, the IPN may contain a polymerhaving aromatic moieties, provided that the polymer is not formed from,and does not contain, an oxybenzoic acid and is not present in thecenter or core layer. In another preferred embodiment, the IPN maycontain a polymer having aromatic moieties, provided that the polymer isnot formed from, and does not contain, aromatic hydroxy-acids and is notpresent in the center or core layer.

In a preferred embodiment, the IPN can be formed from a materialcontaining a urethane, an epoxy homopolymer or copolymer, a polymerhaving backbone or pendant ester groups, a polyimide or copolymerincluding imide groups, a polysiloxane or copolymer including siloxanegroups, or a combination thereof. In another preferred embodiment, theIPN can include an acrylate homopolymer or copolymer, an alkyl-acrylatehomopolymer or copolymer, an alkyl alkyl-acrylate homopolymer orcopolymer, a homopolymer or copolymer including vinyl acetate groups, ahomopolymer or copolymer including halogen groups, a homopolymer orcopolymer including a uretdione group, or a combination thereof.

In another embodiment, the golf ball includes a semi-IPN in a portion ofthe golf ball. In this embodiment, the portion of the golf ballcontaining the IPN includes at least one of a center, an intermediatelayer disposed about the center, or a cover layer.

The present invention is also directed to golf balls including an IPNhaving at least two polymeric components, wherein the ΔT_(g) between anytwo of the polymeric components is, in various embodiments, at leastabout 5% lower, at least about 10% lower, at least about 20% lower, atleast about 35% lower, at least about 50% lower, or at least about 75%lower, than the ΔT_(g) between a polymer blend including the same twopolymeric components. In another embodiment, the formation of an IPNyields only one observable T_(g) for the at least two polymericcomponents. ΔT_(g) can be measured by DSC.

The present invention is also directed to golf balls including an IPNhaving at least two polymeric components, at least one of which is acrystallizable polymeric component that exhibits an area under a meltingendotherm at or around its T_(pm) of, in various embodiments, at leastabout 5% lower, at least about 10% lower, at least about 15% lower, atleast about 25% lower, at least about 50% lower, and at least about 75%lower, than the area under the melting endotherm at or around a T_(pm)of a homopolymer of the same crystallizable polymeric component. Inanother embodiment, the formation of an IPN results in at least one ofthe crystallizable polymeric components being substantially free ofcrystallinity, as measured by ΔH_(f). These values are generallyproportional to the relative amount of each polymer present.

In addition, the present invention involves golf balls including an IPNhaving at least two polymeric components, wherein at least one of thepolymeric components exhibits an average phase size, in variousembodiments, at least about 10% smaller, at least about 20% smaller, atleast about 35% smaller, at least about 60% smaller, and at least about85% smaller, than the average phase size of that phase separatedcomponent in a blend or mixture of the at least two components. In somecases, IPN formation can result in complete miscibility of the system,resulting in no discernible phase boundaries, while the components mayhave been immiscible or only partially miscible when in a blend. Thistest is only applicable if a ground polymer, such as a thermoset, is notused to form the polymer blend.

In addition, the present invention relates to golf balls including acover layer which includes an IPN having at least two polymericcomponents, wherein the shear test rating of the cover layer is at least1 rating category lower than that measured for a cover layer including apolymer blend or mixture that is substantially free of IPN and that ismade of the same components as the IPN. In a preferred embodiment, theshear test rating of the cover layer is at most 2.

The present invention is also directed to processes for forming aportion of a golf ball which include: providing a golf ball center anddisposing an IPN about the center to provide a portion of the golf ball.Advantageously, the IPN may be included in an intermediate layerdisposed about the center or in an outer cover layer.

Another aspect of the present invention relates to processes for forminga golf ball including: providing a golf ball center; providing a golfball cover layer disposed over the center; and optionally providing atleast one intermediate layer disposed between the center and the coverlayer. Advantageously, at least a portion of the golf ball may includean interpenetrating polymer network that is non-vulcanizable,non-aromatic, or non-ionomeric. For example, when the golf ball includesa non-vulcanizable IPN, a styrenic moiety can be included on a polymerof the IPN. In another embodiment, the IPN may contain an ionomericpolymer, provided that the ionomeric polymer does not contain acopolymer of an α-olefin and a metal-neutralized α,β-unsaturatedcarboxylic acid and is not present in a cover layer. In one preferredembodiment, the IPN may contain an ionomeric polymer, provided that theionomeric polymer does not contain a copolymer of ethylene and ametal-neutralized α,β-unsaturated carboxylic acid and is not present ina cover layer. In yet another embodiment, the IPN may contain a polymerhaving aromatic moieties, provided that the polymer is not formed from,and does not contain, an oxybenzoic acid and is not present in thecenter or core layer. In another preferred embodiment, the IPN maycontain a polymer having aromatic moieties, provided that the polymer isnot formed from, and does not contain, aromatic hydroxy-acids and is notpresent in the center or core layer.

In preferred embodiments, the IPNs made by these processes include anymaterials suitable for use in the golf balls of the present invention,as listed above.

Another aspect of the invention relates to a method for preparing aportion of a golf ball, which includes: combining at least a first and asecond component, each comprising a monomer, oligomer, prepolymer, or acombination thereof, to form a mixture, wherein the first and the secondcomponents are miscible with each other and are not substantiallyreactive with each other; sufficiently polymerizing each component inthe mixture to form a material containing at least one crosslinkedpolymer; and forming the material into the portion of the golf ball. Inone embodiment, the first component contains a prepolymer. In anotherembodiment, the material contains at least two crosslinked polymers.

Another aspect of the invention relates to golf equipment, at least aportion of which contains at least one interpenetrating polymer network.Advantageously, any portion of golf equipment containing aninterpenetrating polymer network can contain materials identical oranalogous to those used in any portion of a golf ball detailed aboveaccording to the invention.

Another aspect of the invention relates to a method for preparing aportion of golf equipment, which includes: combining at least a firstand a second component, each including a monomer, oligomer, prepolymer,or a combination thereof, to form a mixture, wherein the first and thesecond components are miscible with each other and are not substantiallyreactive with each other; sufficiently polymerizing each component inthe mixture to form a material containing at least one crosslinkedpolymer; and forming the material into the portion of the golfequipment. Advantageously, the invention also relates to any method forpreparing a portion of golf equipment identical or analogous to anymethods for preparing a portion of a golf ball.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention can be ascertained fromthe following detailed description that is provided in connection withthe drawings described below:

FIG. 1 illustrates a golf ball including a center and a cover layerdisposed over the center, in which at least one of the center or thecover layer includes an IPN.

FIG. 2 illustrates a multi-layer golf ball including a center, anintermediate layer disposed over the center, and a cover layer disposedover the intermediate layer, in which at least one part of the golf ballincludes an IPN.

FIG. 3 illustrates a multi-layer golf ball including a core, anintermediate layer, and a cover layer disposed over the core, in whichat least one part of the golf ball includes an IPN.

DEFINITIONS

With respect to the present invention, all percentages are weightpercentages unless otherwise indicated.

As used herein, the term “about” should be understood to modify eitherone or both numbers in a range of values.

As used herein, the term “golf equipment” includes any type of equipmentused in connection with golf, including, but not limited to, golf clubs(i.e., putters, drivers, and wedges) and club attachments, additions, ormodifications, such as striking face inserts; golf club components(e.g., shafts, hosels, and grips); golf club vibration damping devices;golf gloves; golf shoes; and any portion of the above items. For thepurposes of this invention, golf equipment does not include golf balls.

As used herein, the term “fluid” includes a liquid, a paste, a gel, agas, or any combination thereof. A “fluid-filled” golf ball center orcore according to the invention also includes a hollow center or core.

In the context of the present invention, the phrase “substantially freeof” an item means that there is less than about 5%, preferably less thanabout 2%, more preferably less than about 1% of that item present. Mostpreferably, it means that the item is completely free of that item.

In the context of the present invention, the term “prepolymer” refersgenerally to a macromonomer or partially polymerized material formed bythe reaction product of at least two components, each having afunctionality that is reactive with at least one other component underthe appropriate circumstances, which macromonomer or partiallypolymerized material can be subsequently reacted with at least one othercomponent (which may be the same as one of the at least two componentsor different) to form a polymer. In particular, a “prepolymer” may referto a material containing at least one isocyanate-containing componentand at least one isocyanate-reactive component, for example, such as apolyol, a polyamine, an epoxy-containing compound, or a mixture thereof.Alternatively, “prepolymers” according to the present invention may notinclude an isocyanate-containing component.

In the context of the present invention, a component that has a“substantial lack of” an item should be understood to have less thanabout 20%, preferably to have less than about 10%, more preferably to besubstantially free of that item.

As used herein with regard to golf ball properties, the term“compression” refers to Atti compression, which is defined as thedeflection of an object or material relative to the deflection of acalibrated spring, as measured with an Atti Compression Gauge, that iscommercially available from Atti Engineering Corp. of Union City, N.J.Atti compression is typically used to measure the compression of a golfball. When the Atti Gauge is used to measure cores having a diameter ofless than 1.680 inches, it should be understood that a metallic or othersuitable shim is used to make the measured object 1.680 inches indiameter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has now been discovered that golf balls including an interpenetratingpolymer network, or IPN, including at least two polymeric components canadvantageously provide improved golf balls. An interpenetrating polymernetwork useful for the present invention may include two or moredifferent polymers or polymer networks and can encompass any one or moreof the different types of IPNs listed and described below, which mayoverlap:

(1) Sequential interpenetrating polymer networks, in which monomers orprepolymers for synthesizing one polymer or a polymer network arepolymerized in the presence of another polymer or polymer network. Thesenetworks may have been synthesized in the presence of monomers orprepolymers of the one polymer or polymer network, which may have beeninterspersed with the other polymer or polymer network after itsformation or cross-linking;

(2) Simultaneous interpenetrating polymer networks, in which monomers orprepolymers of two or more polymers or polymer networks are mixedtogether and polymerized and/or crosslinked simultaneously, such thatthe reactions of the two polymer networks do not substantially interferewith each other;

(3) Grafted interpenetrating polymer networks, in which the two or morepolymers or polymer networks are formed such that elements of the onepolymer or polymer network are occasionally attached or covalently orionically bonded to elements of an/the other polymer(s) or polymernetwork(s);

(4) Semi-IPNs, in which one polymer is cross-linked to form a networkwhile another polymer is not; the polymerization or crosslinkingreactions of the one polymer may occur in the presence of one or moresets of other monomers, prepolymers, or polymers, or the composition maybe formed by introducing the one or more sets of other monomers,prepolymers, or polymers to the one polymer or polymer network, forexample, by simple mixing, by solublizing the mixture, e.g., in thepresence of a removable solvent, or by swelling the other in the one;

(5) Full, or “true,” interpenetrating polymer networks, in which two ormore polymers or sets of prepolymers or monomers are crosslinked (andthus polymerized) to form two or more interpenetrating crosslinkednetworks made, for example, either simultaneously or sequentially, suchthat the reactions of the two polymer networks do not substantiallyinterfere with each other;

(6) Homo-IPNs, in which one set of prepolymers or polymers can befurther polymerized, if necessary, and simultaneously or subsequentlycrosslinked with two or more different, independent crosslinking agents,which do not react with each other, in order to form two or moreinterpenetrating polymer networks;

(7) Gradient interpenetrating polymer networks, in which either someaspect of the composition, frequently the functionality, the copolymercontent, or the crosslink density of one or more other polymer networksgradually vary from location to location within some, or each, otherinterpenetrating polymer network(s), especially on a macroscopic level;

(8) Thermoplastic interpenetrating polymer networks, in which thecrosslinks in at least one of the polymer systems involve physicalcrosslinks, e.g., such as very strong hydrogen-bonding or the presenceof crystalline or glassy regions or phases within the network or system,instead of chemical or covalent bonds or crosslinks; and

(9) Latex interpenetrating polymer networks, in which at least onepolymer or set of prepolymers or monomers are in the form of latices,frequently (though not exclusively) in a core-shell type of morphology,which form an interpenetrating polymer network when dried, for example,as a coating on a substrate (if multiple polymers or sets of prepolymersor monomers are in the form of latices, this is sometimes called an“interpenetrating elastomer network,” or IEN).

It should be understood that an interpenetrating polymer networkaccording to the invention should not include a copolymer network. Theterm “copolymer network,” as used herein, can be defined as a singlepolymer network formed from two or more different types of monomers,oligomers, precursor packages, or polymers, during which networkformation: a) the crosslinking reaction(s) result(s) in the differenttypes of polymers, oligomers, or precursors being sufficientlyinter-crosslinked, i.e., the polymers, oligomers, or precursors of oneor more types are connected to polymers, oligomers, or precursors of theother different types, such that effectively one crosslinked networkconnecting all the different monomers, oligomers, precursors, orpolymers is formed; b) the contemporaneous or consecutive polymerizationreaction(s) of all the different types of monomers, oligomers, orprecursors result(s) in two or more different types of copolymers, whichmay themselves be oligomeric or polymeric and may be precursors to(an)other type(s) of copolymer(s), and which may then undergointer-crosslinking reaction(s), as in a), between the different types ofcopolymers; c) the contemporaneous or consecutive polymerizationreaction(s) of all the different types of monomers, oligomers, orprecursors result(s) in a single type of copolymer, which may itself beoligomeric or polymeric and may be a precursor to another type ofcopolymer, and which may then undergo a sufficient intra-crosslinkingreaction, i.e., the copolymer chains of the single type are connected toother copolymer chains of the same type, such that effectively a singlecrosslinked network connecting copolymer chains is formed; or d) anycombination thereof.

A grafted IPN is distinguishable from a copolymer network, in that theinter-crosslinking of a grafted IPN is only occasional, resulting inrelatively few cross-type polymer linkages, while the inter-crosslinkingof a copolymer network occurs relatively frequently, resulting in arelatively large amount of cross-type polymer linkages. As a result, thecopolymer network is effectively a single copolymer network, while thegrafted IPN according to the invention may be lightly inter-crosslinkedbut is effectively a combination of at least two, preferablyco-continuous, polymer networks. Preferably, grafted IPNs according tothe invention have a substantial lack of cross-type polymer linkages, orinter-crosslinking. In one embodiment, a layer containing a gradient IPNaccording to the invention has a flexural modulus below about 5 ksi.

With the exception of grafted IPNs above, all forms of crosslinkingrecited in the descriptions of interpenetrating polymer networks aboveshould hereby be understood to be intra-crosslinks, or same-type polymerlinkages, i.e., crosslinks between polymer chains made from the sameprecursor package. Still, grafted IPNs predominantly containintra-crosslinks, but also contain a small amount of inter-crosslinks.

It should also be understood that an interpenetrating polymer networkaccording to the invention should not include a combination of anindividual polymer and a polymer network of essentially the same type asthe individual polymer, i.e., For example, a single type of homopolymeror copolymer, e.g., such as PMMA, that has been: a) incompletelycrosslinked, e.g., such as by incorporation of an appropriate amount ofdiacrylate monomer; or b) incompletely or completely crosslinked andthen blended with uncrosslinked, neat PMMA, is not considered an IPNaccording to the present invention, despite its possiblecharacterization as a semi-homo-IPN. Such a combination is considered apartially-crosslinked, single-polymer network or system.

Generally, IPNs improve the compatibility of polymeric components,especially in comparison to conventional polymer blends. In aninterpenetrating polymer network of the present invention, thecompatibility can be evidenced by comparing experimentally measuredproperties, such as the relative glass transition temperatures (or thedifference between them, denoted as ΔT_(g)) or the relativecrystallinity or crystalline perfection (as represented by the areaunder the melting endotherm), if at least one component of the IPN iscrystallizable. These properties may be experimentally observed by anumber of different instruments, such as a differential scanningcalorimeter (“DSC”) or dynamic mechanical analyzer (“DMA”) or dynamicmechanical thermal analyzer (“DMTA”).

Preferably, the formation of an IPN reduces the ΔT_(g) between at leasttwo of the polymeric components of the IPN at least about 5%, ascompared with the ΔT_(g) between a polymer blend containing the same atleast two polymeric components. In one embodiment, the formation of anIPN reduces the ΔT_(g) between at least two of the polymeric componentsof the IPN at least about 10%. In another embodiment, the formation ofan IPN reduces the ΔT_(g) between at least two of the polymericcomponents of the IPN at least about 20%. In various other embodiments,the formation of an IPN reduces the ΔT_(g) between at least two of thepolymeric components of the IPN at least about 35%, at least about 50%,and at least about 75%. In yet another embodiment, the formation of anIPN yields only one observable T_(g) for the at least two polymericcomponents.

Alternately, in the case where at least two of the polymeric componentsof the IPN associate or interact strongly in a polymer blend, especiallythrough hydrogen-bonding, ionic aggregation, chelation, or the like, theformation of an IPN can increase the ΔT_(g) between the at least twopolymeric components in the IPN, in some cases at least about 5%, ascompared with the ΔT_(g) between a polymer blend containing the same atleast two polymeric components. In one such alternate embodiment, theformation of an IPN increases the ΔT_(g) between at least two of thepolymeric components of the IPN at least about 10%. In another suchalternate embodiment, the formation of an IPN increases the ΔT_(g)between at least two of the polymeric components of the IPN at leastabout 20%.

For example, in the case of a polyurethane-epoxy polymer IPN system, apolymer blend containing the polyurethane and the epoxy polymer can bemade in a number of ways, such as by: grinding a cured epoxy polymerinto a powder; mixing the proper proportion of the powdered epoxypolymer with the urethane precursor package components to uniformlydisperse the epoxy powder, but before polymerization, gelation, orsolidification occurs; and shaping the mixture into a similar shape asthe IPN (e.g., a golf ball or portion thereof). This procedure canadvantageously be used for any blend in which at least one of thepolymeric components is a thermoset material.

Preferably, the formation of an IPN reduces the absolute value of thearea under the melting endotherm, often called ΔH_(f), of at least oneof the crystallizable polymeric components of the IPN at least about 5%less than the area under the melting endotherm of a polymer blend of thesame ratio of the at least one crystallizable polymeric component. Inone embodiment, the formation of an IPN reduces ΔH_(f) of at least oneof the crystallizable polymeric components of the IPN at least about 10%compared to the blend. In another embodiment, the formation of an IPNreduces ΔH_(f) of at least one of the crystallizable polymericcomponents of the IPN at least about 15% compared to the blend. Invarious other embodiments, the formation of an IPN reduces ΔH_(f) of atleast one of the crystallizable polymeric components of the IPN at leastabout 25% compared to the blend, at least about 50% compared to theblend, and at least about 75% compared to the blend. In yet anotherembodiment, the formation of an IPN results in at least one of thecrystallizable polymeric components being substantially free ofcrystallinity, as measured by ΔH_(f).

When performing DMA or DMTA experiments, ASTM D4065-95 was followed inanalyzing sample material responses. A heating rate of no more thanabout 2° C./min was employed for these tests, and the thicknesses of thesamples were kept within about 5% of the average thickness. Whenperforming DSC experiments to measure the glass transition temperature,T_(g), or the melting temperature, T_(pm), of samples, ASTM D3418-99 wasfollowed, in which the numerical value of T_(g) represents the mediantemperature of the transition and the numerical value of T_(pm)represents the peak extremum of the melting endotherm. When performingDSC experiments to measure the degree of crystallinity or the area underthe melting endotherm, ΔH_(f), ASTM D3417-99 was followed.

As is very often the case in multi-polymer blend systems, two of thepolymeric components may be immiscible or partially miscible, such thatphase separation occurs to a certain extent. This phase separation maybe visible to one of ordinary skill in the art (macrophase separation)or may only be observable through specialized characterizationtechniques designed to probe regions of less than about 500 microns(microphase separation). At the meeting of the at least two phases,there is a phase boundary that defines the edge of each phase. Theaverage size of the phases of each phase separated component can beexperimentally measured using, for example, atomic force microscopy,scanning electron microscopy, transmission electron microscopy, or otherappropriate characterization apparatus.

In a preferred embodiment, the formation of an IPN, in which two of thepolymeric components may be immiscible or partially miscible, results inan average phase size of each phase separated component that can beconsiderably less than the average phase size of each phase separatedcomponent in a blend of two or more of the components. In oneembodiment, the formation of an IPN results in an average phase size ofeach phase separated component being at least about 10% smaller than ablend of the two components. In another embodiment, the formation of anIPN results in an average phase size of each phase separated componentbeing at least about 20% smaller than a blend of the two components. Invarious other embodiments, the formation of an IPN results in an averagephase size of each phase separated component being at least about 35%smaller than a blend of the two components, at least about 60% smallerthan a blend of the two components, and at least about 85% smaller thana blend of the two components. In some cases, IPN formation can resultin complete miscibility of the system, resulting in no discernible phaseboundaries, while the components may have been immiscible or onlypartially miscible when in a blend.

In one embodiment, the formation of an IPN increases at least one of thefollowing measurable quantities: the area under the loss modulus peak,represented by a local maximum in E″, or loss tangent peak, representedby a local maximum in tan δ; the temperature range over which the lossmodulus or loss tangent peak extends; the full-width at half-maximumheight (FWHM) of the loss modulus or loss tangent peak; or the number ofloss modulus or loss tangent peaks over a given temperature interval, ascompared to the same value(s) measured for a blend of the same ratio ofthe at least two IPN components. In another embodiment, the formation ofan IPN increases at least one of the aforementioned measurablequantities by at least about 2%, as compared to the same value(s)measured for a blend of the same ratio of the at least two IPNcomponents. In yet another embodiment, the formation of an IPN increasesat least one of the aforementioned measurable quantities by at leastabout 5%, as compared to the same value(s) measured for a blend of thesame ratio of the at least two IPN components. In still anotherembodiment, the formation of an IPN increases at least one of theaforementioned measurable quantities by at least about 10%, as comparedto the same value(s) measured for a blend of the same ratio of the atleast two IPN components. In various other embodiments, the formation ofan IPN increases at least one of the aforementioned measurablequantities by at least about 25%, by at least about 50%, and by at leastabout 75%, as compared to the same value(s) measured for a blend of thesame ratio of the at least two IPN components. Alternately, instead of acomparison to the value(s) measured for a blend of the same ratio of theat least two IPN components, at least one of the aforementioned measurequantities can be compared to an uncrosslinked polymer of one of the atleast two IPN components, a crosslinked polymer of one of the at leasttwo IPN components, a random, block, graft, or other type of copolymerof at least two of the individual polymer components of the IPN, acrosslinked copolymer of at least two of the individual polymercomponents of the IPN, or some combination thereof.

It is also desirable for the cover, or the outermost layer of the coverif the cover has a plurality of layers, to exhibit a high shearresistance, which is manifest as the ability of a material to maintainits mechanical stability and integrity upon the application of a shearstress to that material. A “shear resistance rating” is a qualitative,or relative, scale for assessing the relative shear resistance of amaterial. The lower the shear resistance rating is, the higher the shearresistance of the material. For painted golf ball cover materials, theshear resistance rating categories from 1 to 5 are listed and describedin the table below:

Description Rating No visible damage to cover or paint 1 Paint damageonly 2 Slight cover shear and/or paint damage observed 3 Moderate covershear; fraying; and/or slight material removed 4 Extensive cover shear;heavy material removed; and/or severe 5 material clumping

The shear resistance rating can be determined by using a Miya™mechanical Golf Swing Machine, commercially available from Miyamae Co.,Ltd., of Osaka, Japan, to make two hits on each of about 6 to 12substantially identical golf balls of substantially the same compositionwith either a sand wedge or a pitching wedge. First, the test conditionsare adjusted and verified so that a control golf ball having a balatacover produces a rating of 5 on the shear resistance rating scale above.Following the calibration procedure, each experimental golf ball istested and assigned a rating based upon visible manifestations of damageafter being struck. The shear resistance rating for a golf ball coverlayer of a given composition represents a numerical average of all thetested substantially identical golf balls. One alternative way to testshear resistance of a golf ball cover involves using player-testing andevaluating the results after the ball is struck multiple times withwedges and/or short irons.

In a preferred embodiment, the formation of an IPN in a layer of a golfball according to the present invention increases the shear resistanceof the cover layer of that golf ball, preferably resulting in a decreasein the shear test rating of at least 1, more preferably resulting in adecrease of at least 2, compared to the cover layer material of aconventional golf ball that is substantially free of IPN and that ismade of the same components as the IPN. In that embodiment, it ispreferred that the shear resistance of the cover layer of that golf ballhas a shear test rating of at most 3, most preferably of at most 2.

Advantageously, the formation of an IPN in a golf ball layer may alsoincrease the resistance to moisture penetration of that layer. IPNformation in that layer may also provide reduction in the water vaporpermeability of a golf ball layer having an IPN therein. The reducedexposure of golf ball materials to water or water vapor helps inhibitdegradation of or maintain the mechanical and/or chemical properties ofthose materials. This is particularly true when the water or moisturecan facilitate degradation of molecular weight or mechanical propertiesof one or more components of the materials within the golf ball.

The ranges of values of several golf ball or material properties listedherein can vary, even outside their recited ranges, by the inclusion ofIPNs according to the invention and, if necessary, by selectivelyvarying at least one other property mentioned herein. Examples of suchgolf ball or material properties whose ranges can be varied by inclusionof an IPN include, but are not limited to, tensile or flexural modulusand impact resistance.

IPNs according to the present invention include at least two precursorpackages, which correspond to the at least two polymer components ornetworks. Each precursor package contains at least all the compoundsnecessary to form one of the polymerized components of the IPN.Compounds that may be used in a precursor package include any monomers,oligomers, or pre-polymers that are to be attached to the polymercomponent by polymerization. Most notably in polyurethane-containingsystems, a chain extender component is also included to further linearlyextend a pre-polymer component.

When referring to polymers synthesized by step-growth polymerization, itshould be understood that monomers, oligomers, and pre-polymers refer toany or all compounds with functional groups that participate in thepolymerization and are attached to the resulting step-growth homopolymeror copolymer.

Although some polymers may be formed through self-polymerization, forexample, such as polystyrene from styrene monomer, when activated byheat or the appropriate energy, most chain growth polymerizationsinvolve an initiator. The choice of initiator of use in the presentinvention depends on each polymer component to be synthesized, and anyavailable initiator capable of polymerizing the selected monomers,oligomers, or pre-polymers are generally also present in a precursorpackage. Suitable initiators can include, for example, free radical orionic initiators, such as di(2-t-butyl-peroxyisopropyl)benzene,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide,di-t-butyl peroxide, di-t-amyl peroxide,2,5-di-(t-butylperoxy)-2,5-dimethyl hexane,n-butyl-4,4-bis(t-butylperoxy)valerate, lauryl peroxide, benzoylperoxide, t-butyl hydroperoxide, 4,4′-azobis(isobutyronitrile),4,4′-azobis(cyanovalerate), 4,4′-azobis(cyanovaleric acid), otherazo-compounds, azides, sec-butyllithium, n-butyllithium, otheralkyllithiums, aryllithiums, and mixtures thereof. In one embodiment,the free radical initiator is an inhibitor-containing peroxide, such as2,6-di-t-butylbenzoquinone,2,6-di-t-butyl-4-methylene-2,5-cyclohexadiene-1-one,2,6-di-t-butyl-4-hydroxybenzaldehyde, 2,6-di-t-butyl-4-isopropylphenol,4,4′-methylene bis-(2,6-di-t-butylphenol),1,2-bis-(3,5-di-t-butyl-4-hydroxyphenyl)ethane,2,3,5,6-tetramethylbenzoquinone, 2-t-butylhydroquinone,2,2′-methylenebis-(4-methyl-6-t-butylphenol), and the like, and mixturesthereof. The free-radical initiator is generally present in an amountsufficient to initiate a polymerization resulting in a polymer having anumber average molecular weight suitable for use in golf balls, which istypically from about 1,000 and 10,000,000 grams/mole. Alternately, thefree radical initiator may be present in an amount greater than about0.1 parts per hundred of the polymer component, preferably about 0.1 to15 parts per hundred of the polymer component, and more preferably about0.2 to 5 parts per hundred of the total polymer component. Thefree-radical source may alternatively or additionally be one or more ofan electron beam, UV or gamma radiation, x-rays, or any other highenergy radiation source capable of generating free radicals. It shouldbe further understood that heat often facilitates initiation of thegeneration of free radicals in the aforementioned compounds.

Optionally, accelerators or catalysts may be included in a precursorpackage to control the speed and/or duration of polymerization and/orcrosslinking reaction(s), if a particular component is crosslinked. Anyaccelerator or catalyst known to one of ordinary skill in the art or anystandard accelerator or catalyst may be used in a precursor package inthe present invention. It should be understood that the accelerator orcatalyst used in a given precursor package should be chosen based on thespecifics of the starting materials, polymerization scheme, andcrosslinking reaction, used to synthesize each polymer component ornetwork. In one embodiment, a carboxylic acid compound may be used as anaccelerator, particularly when one of the polymer components is apolyurethane.

Suitable catalysts include, but are not limited to, Lewis acids, forexample, such as halides of boron, aluminum, indium, tin, antimony, anytransition metal, particularly vanadium, zinc, zirconium, indium,manganese, molybdenum, cobalt, titanium, or tungsten, or mixturesthereof. Exemplary catalysts include chlorides and fluorides of boron,aluminum, or titanium, or mixtures thereof, and more preferably includeboron trifluoride, aluminum trichloride, titanium (III) or (IV)chloride, or mixtures thereof. Other suitable catalysts include, but arenot limited to, Lewis bases, inorganic bases, primary and secondaryamines, and amides. Lewis bases are those compounds containing an atomwith an unshared electron pair in its outer orbital. They are attractedto areas of reduced electron density in the molecules with which theyreact. The organic bases, such as tertiary amines (R3N:), arerepresentative of the more reactive-type Lewis bases suitable for curingepoxy resins. Catalysts may also include mixtures of any of these listedcompounds with one or more other components.

Optionally, additional curing agents may be added to a precursor packageto facilitate the curing of a polymer component. “Curing agents,” asused herein, means any compound, or combination thereof, capable ofconnecting at least two polymeric or oligomeric chains, precursors, ormacromonomers together under appropriate circumstances. For example, instep-growth or condensation polymers, e.g., such as urethane- orurea-containing systems, a curing agent may serve to build the linearmolecular weight of a single polymer molecule, to create, e.g., acrosslinked urethane/urea network, or both. As another example, inepoxy-containing systems, a curing agent may simultaneously facilitatepolymerization and network formation. In most other types of polymers,frequently formed through addition polymerization, curing agents serveonly to crosslink polymers that have already been fully or desirablypolymerized.

Curing agents can be referred to as either “chain extenders,”“crosslinkers,” or both. Suitable chain extenders may vary depending onthe polymers or networks included in the IPN, but, for step-growth orcondensation polymers or epoxies, generally include a polyol, including,for example, telechelic diols, telechelic alkanediols, such as ethyleneglycol, 1,4-butanediol, 1,6-hexanediol, and the like, or mixturesthereof; a polyamine, including, for example, telechelic diamines,telechelic alkanediamines, such as ethylenediamine, propylenediamine,and the like, or mixtures thereof, a cyclic polyol or polyamine, forexample, such as diaminocyclohexane; or mixtures thereof. Suitablecrosslinkers may also vary depending or networks included in the IPN,and include, but are not limited to any chain extender; a disulfide orpolysulfide; a diisocyanate or polyisocyanate; excess diisocyanate orpolyisocyanate; compounds containing or able to generate or activate afree radical; a form of energy able to generate or activate afree-radical, for example, such as heat, visible light, ultravioletlight, x-rays, γ-rays, other energy or radiation, or a mixture thereof;divalent or multivalent salts; or a mixture thereof. In addition, in oneembodiment, the crosslinking of a network, instead of, or in additionto, covalent or ionic crosslinks, may include physical crosslinks, forexample, such as those formed by hydrogen-bonding, provided that the IPNformed has the ability to substantially hold its shape at or around 25°C.

Other curing agents may be reactive upon addition to a precursor packageor to a polymer component or may require activation of some sort tobegin curing. Certain IPN precursors, prepolymers, or polymers, when theproper activators or initiators are used, as understood by those ofordinary skill in the art, can undergo self-polymerization, to formhigher molecular weight polymers, or self-crosslinking, to form anetwork structure, or both. These self-reactions may advantageously befacilitated by one or more catalysts.

Certain curing agents may already be present in a precursor package asthey may derive from a functional group or active site on a polymercomponent. Other curing agents may also be comonomers, for example, suchas multifunctional compounds in step-growth polymerization reactions,such as polyamines, polyisocyanates, polyols, or the like, or mixturesthereof, or compounds containing two sites across which an additionpolymerization may proceed, such as conjugated dienes, non-conjugateddienes, divinyl compounds, conjugated or non-conjugated cycliccompounds, divalent or multivalent salts, or mixtures thereof. One ofordinary skill in the art should be able to determine for a particularIPN system whether certain curing agents function as chain extenders,crosslinkers, or both. It should be understood that any curing agentsalready present in a precursor package or useful in another capacity inthe polymer component of the IPN system shall not be consideredadditional curing agents for that polymer component.

Other compounds useful in polymerization of IPN components may also beoptionally added to a precursor package as the situation warrants, whichcompounds should generally be chosen based on the specifics of thestarting materials, polymerization scheme, and crosslinking reaction,used to synthesize each polymer component or network. For example,density-modifying fillers, antioxidants, processing aids, processingoils, plasticizers, dyes and pigments, as well as other additives wellknown to the skilled artisan may optionally be added to a precursorpackage of the present invention in amounts sufficient to achieve thepurpose for which they are typically used. It should also be noted thatthese other compounds should typically not significantly degrade or becounterproductive toward polymerization or network formation of othercomponents in the IPNs of the present invention.

IPNs of the present invention contain two or more polymers, at least oneof which is crosslinked to form a network. In considering polymersuseful in golf balls of the present invention, examples may includecrosslinked or uncrosslinked incarnations of any polymer capable ofbeing incorporated into an interpenetrating polymer network.

Particularly exemplary polymers include, but are not limited to,urethane polymers or copolymers, polymers made from an epoxy-containingprecursor, polymers having backbone or pendant ester groups, polyimidesor copolymers containing imide groups, polymers or copolymers containingsiloxane groups, polymers or copolymers containing silane groups,acrylate polymers or copolymers (including, but not limited to, mono-,di-, tri, and/or tetra-acrylates), alkyl acrylate polymers orcopolymers, alkyl alkyl-acrylate polymers or copolymers, for example,such as poly(methyl methacrylate) and the like, polyacrylic acids orpoly(alkyl-acrylic acids), including, but not limited to, monomers suchas acrylic acid or methaerylic acid, polymers or copolymers containingvinyl acetate repeat units, polymers or copolymers containing halogengroups, polymers or copolymers containing a uretdione group, polymers orcopolymers containing an oxazolidone group, or mixtures thereof. Otherexamples of useful polymers may include polymers or copolymerscontaining or made from a conjugated diene, polymers or copolymerscontaining a styrenic moiety, ionomeric polymers or copolymers, ormixtures thereof.

In one embodiment, an IPN according to the invention may include anacrylate homopolymer or copolymer or a homopolymer or copolymercontaining a conjugated diene, especially polybutadiene, but may notinclude both.

When a urethane polymer and a polymer made from an epoxy-containingprecursor are both present in an IPN of the present invention, it ispreferable that at least about 50% by weight of the IPN include theurethane polymer network, more preferably at least about 80%, mostpreferably at least about 90%, for golf ball applications.

Interpenetrating polymer networks according to the present invention maytypically be fabricated by a number of different methods known to one ofordinary skill in the art. Such fabrication processes include, but arenot limited to, the following groups of methods.

(1) At least two sets of pre-synthesized oligomeric or polymericcomponents are mixed together by any standard method or any method knownto one of ordinary skill in the art, such as, for example, melt mixing,solvating at least one component in a solution of at least one of theother components and a solvent or solvent mixture, or forming a solutionmixture from at least two solutions, each containing at least one set ofcomponents and a solvent or solvent mixture. In cases where solventmixing is involved, the majority of the solvent or solvent mixtureshould be removed after mixing, for example, by evaporation, boiling,precipitation of the non-solvent components, or the like, preferablysuch that the IPN contains less than 10% solvent, or more preferably issubstantially free of solvent. The mixing process should allow forsufficiently intimate mixing of the components, for example, such thatthe at least two components are at least partially co-entangled. Atleast one of the at least two intimately mixed components can then becrosslinked. If both components are to be crosslinked, the crosslinkingcan occur simultaneously or sequentially.

(2) At least one non-polymerized precursor package can be incorporatedinto at least one other pre-synthesized oligomeric or polymericcomponent, which may or may not already be a crosslinked network, whichincorporation can occur by any method that facilitates intimate mixingof the at least one precursor package with the at least onepre-synthesized component, for example, such as by swelling the at leastone pre-synthesized component with the at least one precursor package,optionally under an applied pressure. Once the components are intimatelymixed, the at least one precursor package can then be appropriatelypolymerized. In the event that the at least one pre-synthesizedcomponent is/are already crosslinked and a semi-IPN is desired, afurther crosslinking reaction may not be necessary. Otherwise, at leastone component of the at least one precursor package, now polymerized,may be crosslinked. Alternately, at least one component of the at leastone precursor package may be crosslinked and polymerized simultaneously.If the at least one pre-synthesized component is/are not alreadycrosslinked, then the at least one pre-synthesized component and the atleast one polymerized precursor package component may be crosslinkedsimultaneously or sequentially. Alternately, if the at least onepre-synthesized component is/are not already crosslinked and a semi-IPNis desired, at least one of either set of components can be crosslinked.

(3) The at least two precursor packages can be mixed together by anymethod that facilitates intimate mixing of the compounds in the at leasttwo precursor packages. The at least two intimately mixed precursorpackages can then be polymerized and/or crosslinked in any order to forman IPN of the present invention. In one embodiment, the at least twoprecursor packages can be polymerized simultaneously or sequentially,but not crosslinked, yielding an intimately mixed blend of the at leasttwo polymerized precursor package components. Then, one or more of thepolymerized components can be crosslinked by an appropriate crosslinkingmethod, and, if more than one of the polymerized components are to becrosslinked, the crosslinking can be done simultaneously orsequentially. Alternately, for one or more of the polymerizedcomponents, the crosslinking reaction may occur simultaneously with thepolymerization reaction. In another embodiment, at least one of the atleast two intimately mixed precursor packages can be polymerized andcrosslinked in the presence of the other precursor package(s), afterwhich the subsequent steps are similar to method #2 (after the initialintimate mixing).

It should be understood that certain rapid-forming IPN systems may needto be prepared using a quick-forming process, such as reaction injectionmolding (RIM), which is a processing method known for use in formingarticles or materials out of rapidly curing polymer systems. Thus, thefaster the formation of a given IPN system, the more suitable the use ofRIM to process it. Indeed, if the IPN gelation time is less than about60 seconds, preferably less than about 30 seconds, RIM is preferred overother conventional processing techniques. In the RIM process, at leasttwo or more reactive, low-viscosity, liquid components are generallymixed, for example, by impingement, and injected under high pressure(e.g., at or above about 1200 psi) into a mold. The reaction times forRIM systems are much faster than in conventional lower-pressure mixingand metering equipment. The precursor packages used for the RIM process,therefore, are typically much lower in viscosity to better facilitateintimate mixing in a very short time.

(4) Each of the at least two precursor packages can be at leastpartially polymerized separately, and preferably simultaneously, atwhich point the at least partially polymerized precursor packages can bemixed together in a manner sufficient to result in intimate mixing ofthe components of the at least two, at-least-partially-polymerizedcomponents. In some urethane-epoxy systems, the total gelation time mayrange from about 40 to 100 seconds. The remainder of the polymerizationsof the intimately mixed components then occur simultaneously, althoughone polymerization may be sufficiently complete before any other. Then,after all polymerizations are sufficiently complete, one or more of thepolymerized components can be crosslinked by an appropriate crosslinkingmethod, and, if more than one of the polymerized components are to becrosslinked, the crosslinking can be done simultaneously orsequentially. Alternately, for one or more of the polymerizedcomponents, the crosslinking reaction may occur simultaneously with thepolymerization reaction.

Crosslinking agents for each of the components, if necessary, may bemixed in with the pre-synthesized components initially, especially ifthey need to be externally activated, or may be added subsequent to theintimate mixing step, especially to avoid premature crosslinking byheating or exposure to activating energy or compounds. If activation isneeded for crosslinking one or more of the at least two intimately mixedcomponents, it is typically performed after an intimate mixing step.Activators for crosslinking may affect an agent or a part of thecomponent itself, for example, such as a carbon-carbon double bond or alabile carbon-hydrogen bond, and generally include, but are not limitedto, heat, light, UV radiation, x-rays, microwave radiation, and gammaradiation.

It should be understood that each method of crosslinking should bechosen to match up with the choice of starting materials andpolymerization scheme used to synthesize each polymer component. Itshould also be noted that each method of crosslinking should typicallynot significantly degrade or be counterproductive toward polymerizationor network formation of other components in the IPNs of the presentinvention.

In one preferred embodiment, the precursor packages are mixed separatelyuntil a sufficient viscosity is attained, preferably from about 2,000cPs to 35,000 cPs, more preferably from about 8,000 cPs to 30,000 cPs,most preferably from about 15,000 cPs to 26,000 cPs.

The golf balls of the present invention can likewise include one or morehomopolymeric or copolymeric thermoplastic or thermoset materials in acenter, an intermediate layer, and/or a cover, either individually or incombination with any other available materials or in a blend with anyIPN according to the invention. In one embodiment, the one or moreportions of the ball including IPN material will not include blends withconventional materials. One of ordinary skill in the art would know thatmost of the polymeric materials listed below may belong in thethermoplastic category or in the thermoset category, depending upon thenature of the repeat units, functional groups pendant from the repeatunits, method of polymerization, method of formation, temperature offormation, post-polymerization treatments, and/or many other possiblefactors, and are suitable for use in golf balls according to theinvention. The materials include, but are not limited to, the followingpolymers, or their set of monomeric, oligomeric, or macromonomericprecursors:

(1) Vinyl resins, for example, such as those formed by thepolymerization of vinyl chloride, or by the copolymerization of vinylchloride with vinyl acetate, acrylic esters or vinylidene chloride;

(2) Polyolefins, for example, such as polyethylene, polypropylene,polybutylene, and copolymers, such as ethylene methylacrylate, ethyleneethylacrylate, ethylene vinyl acetate, ethylene methacrylic acid,ethylene acrylic acid, or propylene acrylic acid, as well as copolymersand homopolymers, such as those produced using a single-site catalyst ora metallocene catalyst;

(3) Polyurethanes, for example, such as those prepared from diols,triols, or polyols and diisocyanates, triisocyanates, orpolyisocyanates, as well as those disclosed in U.S. Pat. No. 5,334,673;

(4) Polyureas, for example, such as those prepared from diamines,triamines, or polyamines and diisocyanates, triisocyanates, orpolyisocyanates, as well as those disclosed in U.S. Pat. No. 5,484,870;

(5) Polyamides, for example, such as poly(hexamethylene adipamide) andothers prepared from diamines and dibasic acids, as well as those fromamino acids such as poly(caprolactam), and blends of polyamides withSURLYN, polyethylene, ethylene copolymers,ethyl-propylene-non-conjugated diene terpolymer, and the like;

(6) Acrylic resins and blends of these resins with, for example,polymers such as poly vinyl chloride, elastomers, and the like;

(7) Olefinic rubbers, for example, such as blends of polyolefins withethylene-propylene-non-conjugated diene terpolymer; block copolymers ofstyrene and butadiene, isoprene or ethylene-butylene rubber; orcopoly(ether-amide), such as PEBAX, sold by ELF Atochem of Philadelphia,Pa.;

(8) Polyphenylene oxide resins or blends of polyphenylene oxide withhigh impact polystyrene, for example, as sold under the trademark NORYLby General Electric Company of Pittsfield, Mass.;

(9) Polyesters, for example, such as polyethylene terephthalate,polybutylene terephthalate, polyethylene terephthalate/glycol modifiedand elastomers, such as sold under the trademarks HYTREL by E.I. DuPontde Nemours & Co. of Wilmington, Del., and LOMOD by General ElectricCompany of Pittsfield, Mass.;

(10) Blends and alloys, for example including polycarbonate withacrylonitrile butadiene styrene, polybutylene terephthalate,polyethylene terephthalate, styrene maleic anhydride, polyethylene,elastomers, and the like, and polyvinyl chloride with acrylonitrilebutadiene styrene, ethylene vinyl acetate, or other elastomers;

(11) Blends of vulcanized, unvulcanized, or non-vulcanizable rubberswith polyethylene, propylene, polyacetal, nylon, polyesters, celluloseesters, and the like; and

(12) Polymers or copolymers possessing epoxy-containing, orpost-polymerization epoxy-functionalized, repeat units, for example, incombination with anhydride, ester, amide, amine, imide, carbonate,ether, urethane, urea, α-olefin, conjugated, or acid (optionally totallyor partially neutralized with inorganic salts) comonomers, or copolymersor blends thereof.

The wound layer, if present, is typically disposed about the core andincludes a tensioned thread material. Many different kinds of threadmaterials may be used for the wound layer of the present invention. Thethread may be single-ply or may include two or more plies. Preferably,the thread of the present invention is single-ply. The thread may beselected to have different material properties, dimensions,cross-sectional shapes, and methods of manufacturing. If two or morethreads are used, they may be identical in material and mechanicalproperties or they may be substantially different from each other,either in cross-section shape or size, composition, elongated state, andmechanical or thermal properties. Mechanical properties that may bevaried include resiliency, elastic modulus, and density. Thermalproperties that may be varied include melt temperature, glass transitiontemperature and thermal expansion coefficient.

The tensioned thread material of the wound layer may encompass anysuitable material, but typically includes fiber, glass, carbon,polyether urea, polyether block copolymers, polyester urea, polyesterblock copolymers, syndiotactic- or isotactic-poly(propylene),polyethylene, polyamide, poly(oxymethylene), polyketone, poly(ethyleneterephthalate), poly(p-phenylene terephthalamide), poly(acrylonitrile),diaminodicyclohexylmethane, dodecanedicarboxylic acid, natural rubber,polyisoprene rubber, styrene-butadiene copolymers,styrene-propylene-diene copolymers, another synthetic rubber, or block,graft, random, alternating, brush, multi-arm star, branched, ordendritic copolymers, or mixtures thereof.

Threads used in the present invention may be formed using a variety ofprocesses including conventional calendering and slitting, meltspinning, wet spinning, dry spinning and polymerization spinning. Anyprocess available to one of ordinary skill in the art may be employed toproduce thread materials for use in the wound layer. The tension used inwinding the thread material of the wound layer may be selected asdesired to provide beneficial playing characteristics to the final golfball. The winding tension and elongation may be kept the same or may bevaried throughout the layer. Preferably, the winding occurs at aconsistent level of tension so that the wound layer has consistenttension throughout the layer.

In addition, the winding patterns used for the wound layer can be variedin any way available to those of ordinary skill in the art. Although oneor more threads may be combined to begin forming the wound layer, it ispreferred to use only a single continuous thread.

The cover provides the interface between the ball and a club. Propertiesthat are desirable for the cover include good moldability, high abrasionresistance, high tear strength, high resilience, and good mold release,among others. The cover typically provides good performancecharacteristics and durability.

A free-radical source, often alternatively referred to as a free-radicalinitiator, may optionally be used in one or more layers of the golfballs according to the invention, particularly when a polymer componentincludes a thermoset material. The free-radical source for non-IPNcomponents may be similar to that used in an IPN of the presentinvention or may be selected from the same or other suitable compounds.The free radical source for non-IPN components is preferably a peroxide,more preferably an organic peroxide. The peroxide is typically presentin an amount greater than about 0.1 parts per hundred of the totalpolymer component, preferably about 0.1 to 15 parts per hundred of thepolymer component, and more preferably about 0.2 to 5 parts per hundredof the total polymer component. It should be understood by those ofordinary skill in the art that the presence of certain components mayrequire a larger amount of free-radical source than the amountsdescribed herein. The free radical source may alternatively oradditionally be one or more of an electron beam, UV or gamma radiation,x-rays, or any other high energy radiation source capable of generatingfree radicals. It should be further understood that heat oftenfacilitates initiation of the generation of free radicals when peroxidesare used as a free-radical initiator.

Fillers added to one or more layers of the golf ball typically includeprocessing aids or compounds to affect rheological and mixingproperties, the specific gravity (i.e., density-modifying fillers), themodulus, the tear strength, reinforcement, and the like. A densityadjusting filler may be used to control the moment of inertia, and thusthe initial spin rate of the ball and spin decay. Fillers are typicallypolymeric or inorganic in nature, and, when used, are typically presentin an amount from about 0.1 to 50 weight percent of the layer in whichthey are included. Any suitable filler available to one of ordinaryskill in the art may be used. Exemplary fillers include, but are notlimited to, precipitated hydrated silica; clay; talc; glass fibers;aramid fibers; mica; calcium metasilicate; barium sulfate; zinc sulfide;lithopone; silicates; silicon carbide; diatomaceous earth; polyvinylchloride; carbonates such as calcium carbonate and magnesium carbonate;metals such as titanium, tungsten, aluminum, bismuth, nickel,molybdenum, iron, copper, boron, cobalt, beryllium, zinc, and tin; metalalloys such as steel, brass, bronze, boron carbide whiskers, andtungsten carbide whiskers; metal oxides such as zinc oxide, iron oxide,aluminum oxide, titanium oxide, magnesium oxide, and zirconium oxide;particulate carbonaceous materials such as graphite, carbon black,cotton flock, natural bitumen, cellulose flock, and leather fiber; microballoons such as glass and ceramic; fly ash; cured, ground rubber; orcombinations thereof.

Fillers may also include various foaming agents or blowing agents whichmay be readily selected by one of ordinary skill in the art. Foamedpolymer blends may be formed by blending ceramic or glass microsphereswith polymer material. Polymeric, ceramic, metal, and glass microspheresmay be solid or hollow, and filled or unfilled. Fillers are typicallyalso added to one or more portions of the golf ball to modify thedensity thereof to conform to uniform golf ball standards. Fillers mayalso be used to modify the weight of the center or at least oneadditional layer for specialty balls, e.g., a lower weight ball ispreferred for a player having a low swing speed.

Methods for measuring the resiliency of golf balls are well known bythose of ordinary skill in the art. One method of measuring theresiliency of a ball at impact is to utilize an air cannon or othermeans of propelling a ball at velocities equivalent to those of a golfclub head. The balls are fired at a massive rigid block, with theinbound and outbound velocities being measured. The velocity may bemeasured by the use of light screens, which measure the time requiredfor the ball to travel a fixed distance. The fixed distance divided bythe transit time is equivalent to the average velocity of the ball overthe fixed distance. The ratio of the outbound velocity to the inboundvelocity is commonly referred to as the coefficient of restitution(“COR”). The COR is a direct measure of the resilience of a golf ball ata particular inbound velocity. Since golf balls behave in a relativelylinear viscoelastic fashion, inbound ball velocity is typicallyfunctionally equivalent to club swing speed, which is set in thestandardized COR test at about 125 ft/sec.

The resultant golf balls prepared according to the invention typicallywill have dimple coverage greater than about 60 percent, preferablygreater than about 65 percent, and more preferably greater than about 70percent. The golf balls typically have a coefficient of restitution ofgreater than about 0.7, preferably greater than about 0.75, and morepreferably greater than about 0.78. The golf balls also typically have acompression of no greater than about 120. In one preferred embodiment,the compression is at least about 40. In another preferred embodiment,the compression is from about 50 to 120, preferably from about 60 to100. The golf ball layers containing the IPNs according to the presentinvention typically have a material hardness greater than about 15 ShoreA, preferably from about 15 Shore A to 85 Shore D. In one preferredembodiment, the material hardness is from about 10 to 85 Shore D.

Additionally, the butadiene rubber that may be used in one or morelayers of the golf balls prepared according to the present invention, inan uncured state, typically has a Mooney viscosity greater than about20, preferably greater than about 30, and more preferably greater thanabout 40. Mooney viscosity is typically measured according to ASTMD1646-99.

Any size golf ball may be formed according to the invention, althoughthe golf ball preferably meets USGA standards of size and weight. Forexample, the final golf ball should preferably have an outer diameter ofat least about 1.68 inches (43 mm) to 1.74 inches (44 mm).

Referring to FIG. 1, a golf ball 10 of the present invention can includea center 12 and a cover 16 surrounding the center 12. Referring to FIG.2, a golf ball 20 of the present invention can include a center 22, acover 26, and at least one intermediate layer 24 disposed between thecover and the center. In one embodiment, the intermediate layer 24 isdisposed within the core, which also includes a center 22 and mayoptionally include a wound layer (not shown). In another embodiment, theintermediate layer 24 is disposed outside of the core, which mayoptionally include a wound layer (not shown), but which is disposedunder the cover layer 26. Each of the cover and center layers in FIG. 1or 2 may include more than one layer; i.e., the golf ball can be aconventional three-piece wound ball, a two-piece ball, a ball having amulti-layer core and an intermediate layer or layers, etc. Also, FIG. 3shows a golf ball 30 of the present invention including a center 32, acover 38, and an intermediate layer 34 located within the core 33.Alternately, also referring to FIG. 3, a golf ball 30 of the presentinvention can include a center 32, a cover 38, and an intermediate layer36 disposed between the cover and the core 33. Although FIG. 3 showsgolf balls with only one intermediate layer, it will be appreciated thatany number or type of intermediate layers may be used whether inside oroutside the core, or both, as desired. Further, any of the FIGS.detailed herein may include embodiments wherein an optional wound layeris disposed between the center and the core of the golf ball.

In the golf balls of any of the aforementioned FIGS., the layercontaining the IPN material may be outside the core or the center, inone embodiment. In another embodiment, the layer containing the IPNmaterial may be inside the cover layer. In yet another embodiment, thelayer containing the IPN material may be in any layer of the golf ball.

EXAMPLES

The following examples are only representative of the methods andmaterials for use in golf ball compositions and golf balls of thisinvention, and are not to be construed as limiting the scope of theinvention in any way.

Example 1 Golf Ball Having a Urethane-Epoxy IPN Present in the CoverLayer

The golf ball of Example 1 was prepared with a 1.585 inch (about 4.03cm) wound core around a fluid-filled center. The golf ball had afinished diameter of about 1.68 inches (about 4.27 cm). The golf ball ofExample 1 included an IPN of a polyurethane and an epoxy polymer,wherein the epoxy polymer component was about 5% of the IPN and thepolyurethane component was about 95% of the IPN. The urethane precursorpackage in Example 1 included Vibrathane B-821 prepolymer,1,4-butanediol, and T-12 dibutyltin dilaurate catalyst. The molarproportion of isocyanate groups in the Vibrathane prepolymer to hydroxylgroups in the diol was in about a 1:0.95 ratio. The epoxy precursorpackage included an epoxy resin (DER 331) and a BF₃ catalyst/curingagent to facilitate self-polymerization and self-crosslinking to form anepoxy network. In order to limit the possibility of the polyurethanebeing further chain extended with the curing agent intended for curingthe epoxy component, the epoxy curing agent was chosen to be catalyticand substantially unreactive with the polyurethane component. The epoxycuring agent chosen to prepare the ball of Example 1 was aBF₃:4-chlorobenzenamine catalyst complex.

The respective precursor packages were mixed separately until asufficient viscosity was achieved to allow mixing by hand, or from about8,000 cPs to 35,000 cPs, after which the precursor packages were mixedtogether and cast as the cover layer on wound cores to form the golfball of Example 1. The total gelation time was about 80 seconds.

TABLE 1 Cover/Ball Characteristics Control Example 1 Urethane componentprecursor Vibrathane/BD Vibrathane/BD package (1:0.95) + 0.01%(1:0.95) + 0.01% T-12 catalyst T-12 catalyst (95%) Epoxy componentprecursor — DER 331/10 pph package BF₃ catalyst (5%) Coefficient ofRestitution 0.81 0.81 Corrected compression 87 90 Material hardness(Shore D) 38 31 Cover hardness (Shore D) 46 43 Initial velocity (ft/sec)255.5 255 T_(g) peak (° C., measured by DSC) −71 −67 T_(g) width (° C.,measured by DSC) 17 24 Vibrathane is an isocyanate end-cappedpolyurethane prepolymer, in this case VIBRATHANE B-821, which is madefrom MDI and a 2,000 M_(n) PTMEG polyol and is available commerciallyfrom Crompton Uniroyal Chemical Company, Inc., of Middlebury, CT; BDrepresents 1,4-butanediol, which is available commercially from BASF ofParsippany, NJ; T-12 represents a dibutyl tin dilaurate catalyst, whichis available commercially from Air Products of Allentown, PA; DER 331represents an epoxy resin based on a diglycidyl ether of bisphenol A(DGEBA) and is commercially available from Dow Chemical Company ofMidland, MI; BF₃ catalyst represents atrifluoroboron-4-chlorobenzenamine catalyst complex and is commerciallyavailable from Air Products of Allentown, PA.

Example 2 Golf Ball Having a Urethane-Polybutadiene Diacrylate IPNPresent in the Cover Layer

The golf ball of Example 2 includes an IPN of a polyurethane and apolybutadiene copolymer, which is prepared with a 1.585 inch (about 4.03cm) wound core around a fluid-filled center. The golf ball has afinished diameter of about 1.68 inches (about 4.27 cm). The golf ball ofExample 2 includes an IPN of a polyurethane and a polybutadienediacrylate copolymer, wherein the polybutadiene copolymer component isabout 10% of the IPN and the polyurethane component is about 90% of theIPN. The urethane precursor package in Example 2 includes VibrathaneB-821 prepolymer, 1,4-butanediol, and T-12 dibutyltin dilauratecatalyst. The molar proportion of isocyanate groups in the Vibrathaneprepolymer to hydroxyl groups in the diol is in about a 1:0.95 ratio.The polybutadiene diacrylate copolymer precursor package includesbutadiene monomer or a polybutadiene resin, a diacrylate crosslinkingagent, and an initiator to facilitate crosslinking to form apolybutadiene diacrylate network. In order to limit the possibility ofdegradation of, or interference with, the polyurethane chain extensionreaction, the polybutadiene diacrylate copolymer crosslinking initiatoris chosen to preferably be substantially unreactive with thepolyurethane. The initiator chosen to prepare the ball of Example 2 is aperoxide initiator, particularly dibenzoyl peroxide.

The respective precursor packages are mixed separately until asufficient viscosity is achieved to allow mixing by hand, or from about8,000 cPs to 35,000 cPs, after which the precursor packages are mixedtogether and cast as the cover layer on wound cores to form the golfball of Example 2.

Example 3 Golf Ball Having a Urethane-Acrylate IPN Present in the CoverLayer

The golf ball of Example 3 is prepared with a 1.585 inch (about 4.03 cm)wound core around a fluid-filled center. The golf ball has a finisheddiameter of about 1.68 inches (about 4.27 cm). The golf ball of Example3 includes an IPN of a polyurethane and an acrylate polymer, wherein theacrylate polymer component is about 10% of the IPN and the polyurethanecomponent is about 90% of the IPN. The urethane precursor package inExample 3 includes Vibrathane B-821 prepolymer, 1,4-butanediol, and T-12dibutyltin dilaurate catalyst. The molar proportion of isocyanate groupsin the Vibrathane prepolymer to hydroxyl groups in the diol is in abouta 1:0.95 ratio. The acrylate precursor package includes methylmethacrylate monomer, optionally a crosslinking agent (such as adiacrylate), and an initiator to facilitate polymerization (andoptionally crosslinking) to form a methyl methacrylate polymer (andoptionally network). In order to limit the possibility of degradationof, or interference with, the polyurethane chain extension reaction, themethyl methacrylate polymerization initiator is chosen to preferably besubstantially unreactive with the polyurethane. The initiator chosen toprepare the ball of Example 3 is a free radical initiator, such asazobisisobutyronitrile (AIBN).

The respective precursor packages are mixed separately until asufficient viscosity is achieved to allow mixing by hand, or from about8,000 cPs to 35,000 cPs, after which the precursor packages are mixedtogether and cast as the cover layer on wound cores to form the golfball of Example 3.

Example 4 Golf Ball Having a Urethane-Epoxy IPN Present in the CoverLayer

The golf ball of Example 4 is prepared with a 1.585 inch (about 4.03 cm)wound core around a fluid-filled center. The golf ball has a finisheddiameter of about 1.68 inches (about 4.27 cm). The golf ball of Example4 includes an IPN of a polyurethane and an epoxy polymer, wherein theepoxy polymer component is about 10% of the IPN and the polyurethanecomponent is about 90% of the IPN. The urethane precursor package inExample 4 includes Vibrathane B-821 prepolymer, 1,4-butanediol, andoptionally a catalyst, such as T-12 dibutyltin dilaurate. The molarproportion of isocyanate groups in the Vibrathane prepolymer to hydroxylgroups in the diol is in about a 1:0.95 ratio. The epoxy precursorpackage includes an epoxy resin (DER 331), a BF₃ catalyst/curing agentto facilitate self-polymerization and self-crosslinking to form an epoxynetwork, and a catalyst to facilitate occasional interreactions of theurethane and the epoxy precursors or networks in the form of oxazolidonefunctional groups. In order to limit the possibility of the polyurethanebeing further chain extended with the curing agent intended for curingthe epoxy component, the epoxy curing agent is chosen to preferably becatalytic and substantially unreactive with the polyurethane component.The epoxy curing agent chosen to prepare the ball of Example 4 is aBF₃:4-chlorobenzenamine catalyst complex. The oxazolidone formationcatalyst chosen to prepare the ball of Example 4 is ethylmethylimidazole.

The respective precursor packages are mixed separately until asufficient viscosity is achieved to allow mixing by hand, or from about8,000 cPs to 35,000 cPs, after which the precursor packages are mixedtogether and cast as the cover layer on wound cores to form the golfball of Example 4.

It is to be understood that the invention is not to be limited to theexact configuration as illustrated and described herein. For example, itshould be apparent that a variety of materials would be suitable for usein the composition or method of making the golf balls according to theDetailed Description of the Preferred Embodiments. Accordingly, allexpedient modifications readily attainable by one of ordinary skill inthe art from the disclosure set forth herein, or by routineexperimentation therefrom, are deemed to be within the spirit and scopeof the invention as defined by the appended claims.

1. A golf ball comprising a core, a cover, and an intermediate layer,wherein the cover layer comprises a non-ionomeric interpenetratingpolymer network formed from a first polymeric component comprisingpolyurethane and a second polymeric component comprisespolybutadienediacrylate copolymer, wherein the IPN exhibits a ΔT_(g)between the first and the second polymeric components at least about 5%less than the ΔT_(g) between a polymer blend comprising the samepolymeric components, and wherein at least one of first and secondpolymeric components is a crystallizable polymeric component thatexhibits an area under a melting endotherm of at least about 2% lessthan the area under the melting endotherm of a homopolymer of the samecrystallizable polymeric component.
 2. The golf ball of claim 1, whereinthe crystallizable polymeric component exhibits an area under a meltingendotherm of at least about 10% less than the area under the meltingendotherm of the homopolymer of the same crystallizable polymericcomponent.
 3. The golf ball of claim 1, wherein the polyurethanecomprises the reaction product of a urethane prepolymer and ahydroxy-terminated curing agent.
 4. The golf ball of claim 1, whereinthe polybutadienediacrylate copolymer comprises the reaction product ofa butadiene monomer or a polybutadiene resin, a diacrylate crosslinkingagent, and an initiator.
 5. The golf ball of claim 4, wherein theinitiator comprises peroxide.
 6. The golf ball of claim 1, wherein theIPN exhibits only one observable T_(g) for the first and secondpolymeric components.
 7. The golf ball of claim 1, wherein the IPNexhibits a ΔT_(g) between any the first and second polymeric componentsat least about 20% less than the ΔT_(g) between a polymer blendcomprising the same polymeric components.
 8. The golf ball of claim 7,wherein the IPN exhibits only one observable T_(g) for the first andsecond polymeric components.
 9. The golf ball of claim 7, wherein theIPN exhibits a ΔT_(g) between the first and second polymeric componentsat least about 50% less than the ΔT_(g) between a polymer blendcomprising the same polymeric components.
 10. The golf ball of claim 9,wherein the IPN exhibits only one observable T_(g) for the first andsecond polymeric components.